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Abstract:

Embodiments of the invention relate to methods and apparatus useful in the
nanopatterning of large area substrates, where a rotatable mask is used
to image a radiation-sensitive material. Typically the rotatable mask
comprises a cylinder. The nanopatterning technique makes use of
Near-Field photolithography, where the mask used to pattern the substrate
is in contact or close proximity with the substrate. The Near-Field
photolithography may make use of an elastomeric phase-shifting mask, or
may employ surface plasmon technology, where a rotating cylinder surface
comprises metal nano holes or nanoparticles.

Claims:

1. A method of near-field nanolithography comprising:a) providing a
substrate having a radiation-sensitive layer on said substrate surface;b)
providing a rotatable mask having a nanopattern on an exterior surface of
said rotatable mask;c) contacting said nanopattern with said
radiation-sensitive layer on said substrate surface;d) distributing
radiation through said nanopattern, while rotating said rotatable mask
over said radiation-sensitive layer, whereby an image having a feature
size ranging from less than 1 μm down to about 1 nm is created in said
radiation-sensitive layer

2. A method in accordance with claim 1, wherein said feature size ranges
from about 100 nm down to 10 nm.

3. A method in accordance with claim 1, wherein said radiation has a
wavelength of 436 nm or less

4. A method in accordance with claim 1, wherein said nanopattern is a
conformable nanopattern, which conforms to said radiation-sensitive layer
on said substrate surface.

5. A method in accordance with claim 4, wherein said conformable
nanopattern is a shaped or nanostructured polymeric material.

6. A method in accordance with claim 3, wherein said rotatable mask is a
phase-shifting mask which causes radiation to form an interference
pattern in said radiation-sensitive

8. A method in accordance with claim 1, wherein said rotatable mask is a
cylinder.

9. A method in accordance with claim 8, wherein said cylinder has a
flexible wall, whereby said cylindrical shape may be deformed upon
contact with said substrate surface.

10. A method in accordance with claim 9, wherein an optically transparent
gas is used to fill said cylinder.

11. A method in accordance with claim 3, wherein said rotatable mask is a
transparent cylinder, whereby radiation may be transmitted from a
location interior of said cylinder.

11. (canceled)

12. A method in accordance with claim 11, wherein said mask is a phase
shifting mask which is present as a relief on a surface of said
transparent cylinder.

13. A method in accordance with claim 11, wherein said mask is a phase
shifting mask which is present on a layer applied over a surface of said
cylinder.

14. A method in accordance with claim 13, wherein at least one
nanopatterned film is applied to an exterior surface of said cylinder,
whereby imaged feature dimensions in said radiation-sensitive layer more
precisely represent prescribed feature dimensions.

15. A method in accordance with claim 8, wherein said substrate is moved
in a direction toward or away from a contact surface of said rotatable
cylinder during distribution of radiation from said contact surface of
said cylinder.

16. A method in accordance with claim 8, wherein said cylinder is rotated
on said substrate while said substrate is static

17. A method in accordance with claim 1, wherein multiple rotating masks
are contacted with a radiation-sensitive layer.

18. A method in accordance with claim 1, wherein said rotatable mask and
said substrate surface are moved independently using a stepper-motor and
a motorized substrate translational mechanism, and wherein movement of
said rotatable mask and said substrate surface are synchronized with each
other, whereby a slip-free contact exposure of said radiation-sensitive
layer is achieved.

19. A method in accordance with claim 1, wherein a liquid is supplied to
an interface between said rotatable mask and said substrate surface.

20. An apparatus to carry out near-field lithography, comprising:a) a
rotatable mask having a nanopattern on an exterior surface of said mask;
andb) a radiation source which supplies radiation of a wavelength of 436
nm or less from said nanopattern, while said nanopattern is in contact
with a radiation-sensitive layer of material.

21. An apparatus in accordance with claim 20, wherein said rotatable mask
is a cylinder.

22. An apparatus in accordance with claim 21, wherein said rotatable mask
is transparent.

23. An apparatus in accordance with claim 22, wherein said rotatable mask
is a phase-shifting mask.

25. An apparatus in accordance with claim 24, wherein a surface of said
mask comprises a metal layer including nanoholes.

25. (canceled)

26. An apparatus in accordance with claim 21, wherein said cylinder is a
flexible cylinder.

27. An apparatus in accordance with claim 26, wherein said flexible
cylinder is filled with an optically transparent gas.

28. An apparatus in accordance with claim 25, wherein multiple cylinders
are present in an arrangement so that said multiple cylinders pass over a
substrate in sequence.

29. An apparatus in accordance with claim 25, wherein multiple cylinders
are present, and wherein a cylinder is present on both the top side and
bottom side of a substrate which is imaged by said apparatus.

30. An apparatus in accordance with claim 29, wherein at least one
cylinder which transmits imaging radiation is present on both the top
side and the bottom side of a substrate which is imaged by said
apparatus.

31. An apparatus in accordance with claim 20, wherein a rotatable mask is
suspended over said substrate by a tensioning device which can be
adjusted to control the amount of force applied to a surface in contact
with said rotatable mask.

Description:

[0002]Embodiments of the invention relate to nanopatterning methods which
can be used to pattern large substrates or substrates such as films which
may be sold as rolled goods. Other embodiments of the invention pertain
to apparatus which may be used to pattern substrates, and which may be
used to carry out method embodiments, including the kind described.

BACKGROUND

[0003]This section describes background subject matter related to the
disclosed embodiments of the present invention. There is no intention,
either express or implied, that the background art discussed in this
section legally constitutes prior art.

[0004]Nanostructuring is necessary for many present applications and
industries and for new technologies which are under development.
Improvements in efficiency can be achieved for current applications in
areas such as solar cells and LEDs, and in next generation data storage
devices, for example and not by way of limitation.

[0006]NanoImprint Lithography (NIL) creates patterns by mechanical
deformation of an imprint resist, followed by subsequent processing. The
imprint resist is typically a monomeric or polymeric formulation that is
cured by heat or by UV light during the imprinting. There are a number of
variations of NIL. However, two of the processes appear to be the most
important. These are Thermoplastic NanoImprint Lithography (TNIL) and
Step and Flash NanoImprint Lithography (SFIL).

[0007]TNIL is the earliest and most mature nanoimprint lithography. In a
standard TNIL process, a thin layer of imprint resist (a thermoplastic
polymer) is spin coated onto a sample substrate. Then a mold, which has
predefined topological patterns, is brought into contact with the sample,
and pressed against the sample under a given pressure. When heated above
the glass transition temperature of the thermoplastic polymer, the
pattern on the mold is pressed into a thermoplastic polymer film melt.
After the sample, with impressed mold is cooled down, the mold is
separated from the sample and the imprint resist is left on the sample
substrate surface. The pattern does not pass through the imprint resist;
there is a residual thickness of unchanged thermoplastic polymer film
remaining on the sample substrate surface. A pattern transfer process,
such as reactive ion etching, can be used to transfer the pattern in the
resist to the underlying substrate. The variation in the residual
thickness of unaltered thermoplastic polymer film presents a problem with
respect to uniformity and optimization of the etch process used to
transfer the pattern to the substrate.

[0008]Tapio Makela et al. of VTT, a technical research center in Finland,
have published information about a custom built laboratory scale
roll-to-roll imprinting tool dedicated to manufacturing of submicron
structures with high throughput. Hitachi and others have developed a
sheet or roll-to-roll prototype NIL machine, and have demonstrated
capability to process 15 meter long sheets. The goal has been to create a
continuous imprint process using belt molding (nickel plated molds) to
imprint polystyrene sheets for large geometry applications such as
membranes for fuel cells, batteries and possibly displays.

[0009]Hua Tan et al of Princeton University have published 2
implementations of roller Nanoimprint lithography: rolling cylinder mold
on flat, solid substrate, and putting a flat mold directly on a substrate
and rolling a smooth roller on top of the mold. Both methods are based on
TNIL approach, where roller temperature is set above the glass transition
temperature, Tg, of the resist (PMMA), while the platform is set to
temperature below Tg. Currently the prototype tools do not offer a
desirable throughput. In addition, there is a need to improve reliability
and repeatability with respect to the imprinted surface.

[0010]In the SFIL process, a UV curable liquid resist is applied to the
sample substrate and the mold is made of a transparent substrate, such as
fused silica After the mold and the sample substrate are pressed
together, the resist is cured using UV light, and becomes solid. After
separation of the mold from the cured resist material, a similar pattern
to that used in TNIL may be used to transfer the pattern to the
underlying sample substrate. Dae-Geun Choi from Korea Institute of
Machinery suggested using fluorinated organic-inorganic hybrid mold as a
stamp for Nanoimprint lithography, which does not require anti-stiction
layer for demolding it from the substrate materials.

[0011]Since Nanoimprint lithography is based on mechanical deformation of
resist, there are a number of challenges with both the SFIL and TNIL
processes, in static, step-and-repeat, or roll-to-roll implementations,.
Those challenges include template lifetime, throughput rate, imprint
layer tolerances, and critical dimension control during transfer of the
pattern to the underlying substrate. The residual, non-imprinted layer
which remains after the imprinting process requires an additional etch
step prior to the main pattern transfer etch. Defects can be produced by
incomplete filling of negative patterns and the shrinkage phenomenon
which often occurs with respect to polymeric materials. Difference in
thermal expansion coefficients between the mold and the substrate cause
lateral strain, and the strain is concentrated at the corner of the
pattern. The strain induces defects and causes fracture defects at the
base part of the pattern mold releasing step.

[0012]Soft lithography is an alternative to Nanoimprint lithography method
of micro and nano fabrication. This technology relates to replica molding
of self assembling monolayers. In soft lithography, an elastomeric stamp
with patterned relief structures on its surface is used to generate
patterns and structures with feature sizes ranging from 30 nm to 100 nm.
The most promising soft lithography technique is microcontact printing
(μCP) with self-assembled monolayers (SAMS). The basic process of
μCP includes: 1. A polydimethylsiloxane (PDMS) mold is dipped into a
solution of a specific material, where the specific material is capable
of forming a self-assembled monolayer (SAM). Such specific materials may
be referred to as an ink. The specific material sticks to a protruding
pattern on the PDMS master surface. 2. The PDMS mold, with the
material-coated surface facing downward, is contacted with a surface of a
metal-coated substrate such as gold or silver, so that only the pattern
on the PDMS mold surface contacts the metal-coated substrate. 3. The
specific material forms a chemical bond with the metal, so that only the
specific material which is on the protruding pattern surface sill remain
on the metal-coated surface after removal of the PDMS mold. The specific
material forms a SAM on the metal-coated substrate which extends above
the metal-coated surface approximately one to two nanometers (just like
ink on a piece of paper). 4. The PDMS mold is removed from the
metal-coated surface of the substrate, leaving the patterned SAM on the
metal-coated surface.

[0013]The best-established specific materials for forming SAMs on gold or
silver-coated surfaces are alkanethiolates. When the substrate surface
contains hydroxyl-terminated moieties such as Si/SiO2,
Al/Al2O3, glass, mica, and plasma-treated polymers,
alkylsiloxanes work well as the specific materials. With respect to the
alkanethiolates, μCP of hexadecanethiol on evaporated thin (10-200 nm
thick) films of gold or silver appears to be the most reproducible
process. While these are the best-known materials for carrying out the
pattern formation, gold and silver are not compatible with
microelectronic devices based on silicon technology, although gold or
silver-containing electrodes or conductive wires may used. Currently,
μCP for SAMS of siloxanes on Si/SiO2 surfaces are not as
tractable as the SAMS of alkanethiolates on gold or silver. The SAMS of
siloxanes on Si/SiO2 often provide disordered SAMs, and in some
cases generate submonolayers or multilayers. Finally, the patterned molds
available for μCP are flat "stamp" surfaces, and reproducible and
reliable printing on large areas not only requires very accurate
stitching of the printed pattern from the mold, but also requires
constant wetting of the stamp with the SAM-forming specific material,
which is quite problematic.

[0014]Optical Lithography does not use mechanical deformation or phase
change of resist materials, like Nanoimprint lithography, and does not
have materials management problems like Soft Lithography, thus providing
better feature replication accuracy and more Manufacturable processing.
Though regular optical lithography is limited in resolution by
diffraction effects some new optical lithography techniques based on near
field evanescent effects have already demonstrated advantages in printing
sub-100 nm structures, though on small areas only. Near-field phase shift
lithography NFPSL involves exposure of a photoresist layer to ultraviolet
(UV) light that passes through an elastomeric phase mask while the mask
is in conformal contact with a photoresist. Bringing an elastomeric phase
mask into contact with a thin layer of photoresist causes the photoresist
to "wet" the surface of the contact surface of the mask. Passing UV light
through the mask while it is in contact with the photoresist exposes the
photoresist to the distribution of light intensity that develops at the
surface of the mask. In the case of a mask with a depth of relief that is
designed to modulate the phase of the transmitted light by π, a local
null in the intensity appears at the step edge of relief. When a positive
photoresist is used, exposure through such a mask, followed by
development, yields a line of photoresist with a width equal to the
characteristic width of the null in intensity. For 365 nm (Near UV) light
in combination with a conventional photoresist, the width o the null in
intensity is approximately 100 nm. A PDMS mask can be used to form a
conformal, atomic scale contact with a flat, solid layer of photoresist.
This contact is established spontaneously upon contact, without applied
pressure. Generalized adhesion forces guide this process and provide a
simple and convenient method of aligning the mask in angle and position
in the direction normal to the photoresist surface, to establish perfect
contact. There is no physical gap with respect to the photoresist. PDMS
is transparent to UV light with wavelengths greater than 300 nm. Passing
light from a mercury lamp (where the main spectral lines are at 355-365
nm) through the PDMS while it is in conformal contact with a layer of
photoresist exposes the photoresist to the intensity distribution that
forms at the mask.

[0015]Yasuhisa Inao, in a presentation entitled "Near-Field Lithography as
a prototype nano-fabrication tool", at the 32nd International Conference
on Micro and Nano Engineering in 2006, described a step-and-repeat
near-field nanolithography developed by Canon, Inc. Near-field
lithography (NFL) is used, where the distance between a mask and the
photoresist to which a pattern is to be transferred are as close as
possible. The initial distance between the mask and a wafer substrate was
set at about 50 μm. The patterning technique was described as a
"tri-layer resist process", using a very thin photoresist. A pattern
transfer mask was attached to the bottom of a pressure vessel and
pressurized to accomplish a "perfect physical contact" between the mask
and a wafer surface. The mask was "deformed to fit to the wafer". The
initial 50 μm distance between the mask and the wafer is said to
allows movement of the mask to another position for exposure and
patterning of areas more than 5 mm×5 mm. The patterning system made
use of i-line (365 nm) radiation from a mercury lamp as a light source. A
successful patterning of a 4 inch silicon wafer with structures smaller
than 50 nm was accomplished by such a step-and-repeat method.

[0016]In an article entitled "Large-area patterning of 50 nm structures on
flexible substrates using near-field 193 nm radiation", JVST B 21 (2002),
at pages 78-81, Kunz et al. applied near-field phase shift mask
lithography to the nanopatterning of flexible sheets (Polyimide films)
using rigid fused silica masks and deep UV wavelength exposure. In a
subsequent article entitled "Experimental and computational studies of
phase shift lithography with binary elastomeric masks", JVST B 24(2)
(2006) at pages 828-835, Maria et al. present experimental and
computational studies of a phase shifting photolithographic technique
that uses binary elastomeric phase masks in conformal contact with layers
of photoresist. The work incorporates optimized masks formed by casting
and curing prepolymers to the elastomer poly(dimethylsiloxane) against
anisotropically etched structures of single crystal silicon on
SiO2/Si. The authors report on the capability of using the PDMS
phase mask to form resist features in the overall geometry of the relief
on the mask.

[0017]U.S. Pat. No. 6,753,131 to Rogers et al, issued Jun. 22, 2004,
titled "Transparent Elastomeric, Contact-Mode Photolithography Mask,
Sensor, and Wavefront Engineering Element", describes a contact-mode
photolithography phase mask which includes a diffracting surface having a
plurality of indentations and protrusions. The protrusions are brought
into contact with a surface of a positive photoresist, and the surface is
exposed o electromagnetic radiation through the phase mask. The phase
shift due to radiation passing through indentations as opposed to the
protrusions is essentially complete. Minima in intensity of
electromagnetic radiation are thereby produced at boundaries between the
indentations and protrusions. The elastomeric mask conforms well to the
surface of the photoresist, and following development of the photoresist,
features smaller than 100 nm can be obtained. (Abstract) In one
embodiment, reflective plates are used exterior to the substrate and the
contact mask, so radiation will be bounced to a desired location at a
shifted phase. In another embodiment, the substrate may be shaped in a
manner which causes a deformation of the phase shifting mask, affecting
the behavior of the phase shifting mask during exposure.

[0018]Near Field Surface Plasmon Lithography (NFSPL) makes use of
near-field excitation to induce photochemical or photophysical changes to
produce nanostructures. The main near-field technique is based on the
local field enhancement around metal nanostructures when illuminated at
the surface plasmon resonance frequency. Plasmon printing consists of the
use of plasmon guided evanescent waves through metallic nanostructures to
produce photochemical and photophysical changes in a layer below the
metallic structure. In particular, visible exposure (λ=410 nm) of
silver nanoparticles in close proximity to a thin film of a g-line
photoresist (AZ-1813 available from AZ-Electronic Materials,
MicroChemicals GmbH, Ulm, Germany) can produce selectively exposed areas
with a diameter smaller than λ/20. W. Srituravanich et al. in an
article entitled "Plasmonic Nanolithography", Nanoletters V4, N6 (2004),
pp. 1085-1088, describes the use of near UV light (λ=230 nm-350 nm)
to excite SPs on a metal substrate, to enhance the transmission through
subwavelength periodic apertures with effectively shorter wavelengths
compared to the excitation light wavelength. A plasmonic mask designed
for lithography in the UV range is composed of an aluminum layer
perforated with 2 dimensional periodic hole arrays and two surrounding
dielectric layers, one on each side. Aluminum is chosen since it can
excite the SPs in the UV range. Quartz is employed as the mask support
substrate, with a poly(methyl methacrylate) spacer layer which acts as
adhesive for the aluminum foil and as a dielectric between the aluminum
and the quartz. Poly(methyl methacrylate is used in combination with
quartz, because their transparency to UV light at the exposure wavelength
(i-line at 365 nm) and comparable dielectric constants (2.18 and 2.30,
quartz and PMMA, respectively). A sub-100 nm dot array pattern on a 170
nm period has been successfully generated using an exposure radiation of
365 nm wavelength. Apparently the total area of patterning was about 5
μm×5 μm, with no scalability issues discussed in the paper.

[0019]Joseph Martin has suggested a proximity masking device for
Near-filed lithography in U.S. Pat. No. 5,928,815, where cylindrical
block covered with metal film for light internal reflection is used for
directing light to the one end of the cylinder (base of the cylinder),
which contains a surface relief pattern used for Near-field exposure.
This block is kept in some proximity distance ("very small, but not
zero") from the photoresist on the sample. Cylinder is translated in
horizontal direction using some precise mechanism, which is used to
pattern photoresist area.

[0020]The only published idea about using rollers for optical lithography
can be found in the Japanese Unexamined Patent Publication, No.
59200419A, published Nov. 13, 1984, titled "Large Area Exposure
Apparatus". Toshio Aoki et al. described the use of a transparent
cylindrical drum which can rotate and translate with an internal light
source and a film of patterned photomask material attached on the outside
of the cylindrical drum. A film of a transparent heat reflective material
is present on the inside of the drum. A substrate with an aluminum film
on its surface and a photoresist overlying the aluminum film is contacted
with the patterned photomask on the drum surface and imaging light is
passed through the photomask to image the photoresist on the surface of
the aluminum film. The photoresist is subsequently developed, to provide
a patterned photoresist. The patterned photoresist is then used as an
etch mask for an aluminum film present on the substrate.

[0021]There is no description regarding the kinds of materials which were
used as a photomask film or as a photoresist on the surface of the
aluminum film. A high pressure mercury lamp light source (500 W) was used
to image the photoresist overlying the aluminum film. Glass substrates
about 210 mm (8.3 in.)×150 mm (5.9 in.) and about 0.2 mm (0.008
in.) thick were produced using the cylindrical drum pattern transfer
apparatus. The feature size of the pattern transferred using the
technique was about 500 μm2, which was apparently a square having
a dimension of about 22.2 μm×22.2 μm. This feature size was
based on the approximate pixel size of an LCD display at the time the
patent application was filed in 1984. The photomask film on the outside
of the cylindrical drum was said to last for approximately 140,000
pattern transfers. The contact lithography scheme used by Toshio Aoki et
al. is not capable of producing sub-micron features.

[0022]It does not appear that an nanoimprinting methods (thermal or
UV-cured) or soft lithography using printing with SAM materials are
highly manufacturable processes. In general, the imprinting method
creates deformation of the substrate material due to the thermal
treatment (thermal NIL, for example) or shrinkage of pattern features
upon polymer curing (UV-cured polymeric features). Moreover, due to the
application of pressure (hard contact) between a stamp and a substrate,
defects are essentially unavoidable, and a stamp has a very limited
lifetime. Soft lithography does have an advantage in that it is thermal
and stress-free printing technology. However, the use of a SAM as an
"ink" for a sub-100 nm pattern is very problematic due to the drifting of
molecules over the surface, and application over large areas has not been
proved experimentally.

SUMMARY

[0023]Embodiments of the invention pertain to methods and apparatus useful
in the nanopatterning of large area substrates ranging from about 200
mm2 to about 1,000,000 mm2, by way of example and not by way of
limitation. In some instances the substrate may be a film, which has a
given width and an undefined length, which is sold on a roll. The
nanopatterning technique makes use of Near-Field UV photolithography,
where the mask used to pattern the substrate is in contact or in very
close proximity (in the evanescent field, less than 100 nm) from the
substrate. The Near-Field photolithography may include a phase-shifting
mask or surface plasmon technology.

[0024]One embodiment the exposure apparatus which includes a
phase-shifting mask in the form of a UV-transparent rotatable mask having
specific phase shifting relief on it's outer surface. In another
embodiment of the phase-shifting mask technology, the transparent
rotatable mask, which is typically a cylinder, may have a polymeric film
which is the phase-shifting mask, and the mask is attached to the
cylinder's outer surface. When it is difficult to obtain good and uniform
contact with the substrate surface, especially for large processing
areas, it is advantageous to have the polymeric film be a conformal,
elastomeric polymeric film such as PMDS, which makes excellent conformal
contact with the substrate through Van-der Waals forces. The polymeric
film phase-shifting mask may consist of multiple layers. Where the outer
layer is nanopatterned to more precisely represent prescribed feature
dimensions in a radiation-sensitive (photosensitive) layer.

[0025]Another embodiment of the exposure apparatus employs a soft
elastomeric photomask material, such as a PDMS film, having
non-transparent features fabricated on one of it's surfaces, which is
attached to the outer surface of the cylinder. Such feature may be chrome
features produced on the PDMS film using one of the lithographic
techniques known in the art.

[0026]In an embodiment of the exposure apparatus which includes surface
plasmon technology, a metal layer or film is laminated or deposited onto
the outer surface of the rotatable mask, which is typically a transparent
cylinder. The metal layer or film has a specific series of through
nanoholes. In another embodiment of the surface plasmon technology, a
layer of metal nanoparticles is deposited on the transparent rotatable
mask's outer surface, to achieve the surface plasmons enhanced
nanopatterning. A radiation source is provided interior to the
transparent cylinder. For example, and not by way of limitation, a UV
lamp may be installed interior of the cylinder. In the alternative, the
radiation source may be placed outside the cylinder, with light from the
radiation source being piped to the interior of the cylinder through one
or both ends of the cylinder. The radiation may be directed from outside
the cylinder or within the cylinder toward particular areas within the
interior of the cylinder using an optical system including mirrors,
lenses, or combinations thereof, for example. Radiation present within
the cylinder may be directed toward the mask substrate contact area using
an optical grating. The radiation may be directed toward the mask
substrate area (coupled) through a waveguide with a grating. The
waveguide or grating is typically placed inside the cylinder, to redirect
radiation toward the contact areas between the cylinder outer surface and
the substrate surface to be imaged.

[0027]In a specialized embodiment of a light source of radiation, an OLED
flexible display may be attached around the exterior of the rotatable
mask, to emit light from each of the pixels toward the substrate. In this
instance the rotatable mask does not need to be transparent. In addition,
the particular pattern to be transferred to a radiation-sensitive
material on the substrate surface may be generated depending on the
application, through control of the light emitted from the OLED. The
pattern to be transferred may be changed "on the fly" without the need to
shut down the manufacturing line.

[0028]To provide high throughput of pattern transfer to a
radiation-sensitive material, and increase the quantity of nanopatterned
surface area, it is helpful to move the substrate or the rotatable mask,
such as a cylinder, against each other. The cylinder is rotated on the
substrate surface when the substrate is static or the substrate is moved
toward the cylinder while the cylinder is static. For reasons discussed
below, there are advantages to moving the substrate toward the cylinder.

[0029]It is important to be able to control the amount of force which
occurs at the contact line between the cylinder and the
radiation-sensitive material on the surface of the substrate (for example
the contact line between an elastomeric nanopatterned film present on the
surface of the cylinder and a photoresist on the substrate surface). To
control this contact line, the cylinder may be supported by a tensioning
device, such as, for example, springs which compensate for the cylinder's
weight. The substrate or cylinder (or both) are moved (upward and
downward) toward each other, so that a spacing between the surfaces is
reduced, until contact is made between the cylinder surface and the
radiation-sensitive material (the elastomeric nanopatterned film and the
photoresist on the substrate surface, for example). The elastomeric
nanopatterned film will create a bond with a photoresist via Van-der
Walls forces. The substrate position is then moved back (downward) to a
position at which the springs are elongated, but the elastomeric
nanopatterned film remains in contact with the photoresist. The substrate
may then be moved toward the cylinder, forcing the cylinder to rotate,
maintaining a dynamic contact between the elastomeric nanopatterned film
and the photoresist on the substrate surface. alternatively, the cylinder
can be rotated and the substrate can be moved independently, but in
synchronous motion, which will assure slip-free contact during dynamic
exposure.

[0030]Multiple cylinders may be combined into one system and arranged to
expose the radiation-sensitive surface of the substrate in a sequential
mode, to provide double, triple, and multiple patterning of the substrate
surface. This exposure technique can be used to provide higher
resolution. The relative positions of the cylinders may be controlled by
interferometer and an appropriate computerized control system.

[0031]In another embodiment, the exposure dose may affect the lithography,
so that an edge lithography (where narrow features can be formed, which
corresponds to a shift of phase in a PDMS mask, for example) can be
changed to a conventional lithography, and the feature size in an imaged
photoresist can be controlled by exposure doze. Such control of the
exposure dose is possible by controlling the radiation source power or
the rotational speed of the cylinder (exposure time). The feature size
produced in the photoresist may also be controlled by changing the
wavelength of the exposure radiation, light source, for example.

[0032]The masks on the cylinders may be oriented by an angle to the
direction of substrate movement. This enables pattern formation in
different directions against the substrate. Two or more cylinders can be
placed in sequence to enable 2D patterns.

[0033]In another embodiment, the transparent cylindrical chamber need not
be rigid, but may be formed from a flexible material which may be
pressurized with an optically transparent gas. The mask may be the
cylinder wall or may be a conformal material present on the surface of
the cylinder wall. This permits the cylinder to be rolled upon a
substrate which is not flat, while making conformal contact with the
substrate surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]So that the manner in which the exemplary embodiments of the present
invention are attained is clear and can be understood in detail, with
reference to the particular description provided above, and with
reference to the detailed description of exemplary embodiments,
applicants have provided illustrating drawings. It is to be appreciated
that drawings are provided only when necessary to understand exemplary
embodiments of the invention and that certain well known processes and
apparatus are not illustrated herein in order not to obscure the
inventive nature of the subject matter of the disclosure.

[0035]FIG. 1A shows a cross-sectional view of one embodiment of an
apparatus 100 useful in patterning of large areas of substrate material,
where a radiation transparent cylinder 106 has a hollow interior 104 in
which a radiation source 102 resides. In this embodiment, the exterior
surface 111 of the cylinder 106 is patterned with a specific surface
relief 112. The cylinder 106 rolls over a radiation sensitive material
108 which overlies a substrate 110.

[0036]FIG. 1B shows a top view of the apparatus and substrate illustrated
in FIG. 1A, where the radiation sensitive material 108 has been imaged
109 by radiation (not shown) passing through surface relief 112.

[0037]FIG. 2 shows a cross-sectional view of another embodiment of an
apparatus 200 useful in patterning of large areas of substrate material.
In FIG. 2, the substrate is a film 208 upon which a pattern is imaged by
radiation which passes through surface relief 212 on a first
(transparent) cylinder 206 while film 208 travels from roll 211 to roll
213. A second cylinder 215 is provided on the backside 209 of film 208 to
control the contact between the film 208 and the first cylinder 206.

[0038]FIG. 3 shows a cross-sectional view of another embodiment of an
apparatus 300 useful in patterning large areas of substrate material. In
FIG. 3, the substrate is a film 308 which travels from roll 311 to roll
313. A first transparent cylinder 306 with surface relief 312 is used to
pattern the topside 310 of film 308, while a second transparent cylinder
326 with surface relief 332 is used to pattern the bottom side 309 of
film 308.

[0039]FIG. 4A shows a cross-sectional view of an embodiment 400 of a
transparent cylinder 406 which includes a hollow center area 404 with an
internal source of radiation 402. The surface relief area 412 is a
conformal structure which includes polymer film 415 with a patterned
surface 413 which is particularly useful for near-field lithography.

[0040]FIG. 4B shows an enlargement of surface 413, which is a surface
relief polymer structure 413 on top of polymeric base material 415. In
FIG. 4B, the polymer base material 415 may be either the same polymeric
material or may be a different polymeric material from the patterned
surface material 413.

[0041]FIG. 5A shows a cross sectional view of an alternative embodiment
500 of surface relief 512 which is present on a hollow transparent
cylinder 506.

[0042]FIG. 5B shows an enlargement of the surface relief 512, which is a
thin metal layer 514 which is patterned with a series of nanoholes 513,
where the metal layer is applied over the exterior surface 511 of hollow
transparent cylinder 506.

[0043]FIG. 5C shows an alternative surface relief 522 which may be used on
the surface of transparent cylinder 506. Surface relief 522 is formed by
metal particles 526 which may be applied directly upon the exterior
surface 511 of hollow transparent cylinder 506 or may be applied on a
transparent film 524 which is attached to the exterior surface 511 of
hollow transparent cylinder 506.

[0044]FIG. 6A is a schematic three dimensional illustration 600 of a
transparent cylinder 604 having a patterned surface 608, where the
cylinder 604 is suspended above a substrate 610 using a tensioning device
602 illustrated as springs.

[0045]FIG. 6B is a schematic of an embodiment 620 where the radiation used
to accomplish imaging is supplied from a radiation source 612 exterior to
cylinder 604, with the radiation distributed internally 615 and 616
within the hollow portion of the cylinder 604.

[0046]FIG. 6c is a schematic of an embodiment 630 where the radiation used
to accomplish imaging is supplied from the exterior radiation source 612
is focused 617 into a waveguide 618 and distributed from the waveguide
618 to an optical grating 621 present on the interior surface 601 of the
cylinder 604.

[0047]FIG. 6D is a schematic of an embodiment 640 where the radiation used
to accomplish imaging is supplied from two exterior radiation sources
612A and 612B, and is focused 621 and 619, respectively upon an optical
grating 621 present on the interior surface 601 of cylinder 604.

[0048]FIG. 7A is a schematic showing the use of multiple cylinders, such
as two cylinders 702 and 704, for example, in series to provide multiple
patterning, which may be used to obtain higher resolution, for example.

[0049]FIG. 7B is a cross-sectional schematic showing a pattern 706 created
by a first cylinder 702 after imaging and development of a
radiation-sensitive material 710. The altered pattern 708 is after
imaging and development of the radiation-sensitive material 710 where the
altered pattern 708 is created by use of the first cylinder 702 in
combination with a second cylinder 704.

[0050]FIG. 8 shows a cross-sectional schematic of a deformable cylinder
800, the interior 804 of which is pressurized using an apparatus 813
which supplies an optically transparent gas. The outer surface 811 of
deformable cylinder 800 may be a nanopatterned/nanostructured film 802 of
a conformable material, which can be rolled upon a non-flat substrate 805
so that radiation from radiation source 902 can be precisely applied over
a surface 816 of substrate 805.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0051]As a preface to the detailed description, it should be noted that,
as used in this specification and the appended claims, the singular forms
"a", "an", and "the" include plural referents, unless the context clearly
dictates otherwise.

[0052]When the word "about" is used herein, this is intended to mean that
the nominal value presented is precise within ±10%.

[0053]Embodiments of the invention relate to methods and apparatus useful
in the nanopatterning of large area substrates, where a rotatable mask is
used to image a radiation-sensitive material. Typically the rotatable
mask comprises a cylinder. The nanopatterning technique makes use of
near-field photolithography, where the wavelength of radiation used to
image a radiation-sensitive layer on a substrate is 650 nm or less, and
where the mask used to pattern the substrate is in contact with the
substrate. The near-field photolithography may make use of a
phase-shifting mask, or nanoparticles on the surface of a transparent
rotating cylinder, or may employ surface plasmon technology, where a
metal layer on the rotating cylinder surface comprises nano holes. The
detailed description provided below is just a sampling of the
possibilities which will be recognized by one skilled in the art upon
reading the disclosure herein.

[0054]Although the rotating mask used to generate a nanopattern within a
layer of radiation-sensitive material may be of any configuration which
is beneficial, and a number of these are described below, a hollow
cylinder is particularly advantageous in terms of imaged substrate
manufacturability at minimal maintenance costs. FIG. 1A shows a
cross-sectional view of one embodiment of an apparatus 100 useful in
patterning of large areas of substrate material, where a radiation
transparent cylinder 106 has a hollow interior 104 in which a radiation
source 102 resides. In this embodiment, the exterior surface 111 of the
cylinder 106 is patterned with a specific surface relief 112. The
cylinder 106 rolls over a radiation sensitive material 108 which overlies
a substrate 110. FIG. 1B shows a top view of the apparatus and substrate
illustrated in FIG. 1A, where the radiation sensitive material 108 has
been imaged 109 by radiation (not shown) passing through surface relief
112. The cylinder is rotating in the direction shown by arrow 118, and
radiation from a radiation source 102 passes through the nanopattern 112
present on the exterior surface 103 of rotating cylinder 106 to image the
radiation-sensitive layer (not shown) on substrate 108, providing an
imaged pattern 109 within the radiation-sensitive layer. The
radiation-sensitive layer is subsequently developed to provide a
nanostructure on the surface of substrate 108. In FIG. 1B, the rotatable
cylinder 106 and the substrate 120 are shown to be independently driven
relative to each other. In another embodiment, the substrate 120 may be
kept in dynamic contact with a rotatable cylinder 106 and moved in a
direction toward or away from a contact surface of the rotatable cylinder
106 to provide motion to an otherwise static rotatable cylinder 106. In
yet another embodiment, the rotatable cylinder 106 may be rotated on a
substrate 120 while the substrate is static.

[0055]The specific surface relief 112 may be etched into the exterior
surface of the transparent rotating cylinder 106. In the alternative, the
specific surface relief 112 may be present on a film of polymeric
material which is adhered to the exterior surface of rotating cylinder
106. The film of polymeric material may be produced by deposition of a
polymeric material onto a mold (master). The master, created on a silicon
substrate, for example, is typically generated using an e-beam direct
writing of a pattern into a photoresist present on the silicon substrate.
Subsequently the pattern is etched into the silicon substrate. The
pattern on the silicon master mold is then replicated into the polymeric
material deposited on the surface of the mold. The polymeric material is
preferably a conformal material, which exhibits sufficient rigidity to
wear well when used as a contact mask against a substrate, but which also
can make excellent contact with the radiation-sensitive material on the
substrate surface. One example of the conformal materials generally used
as a transfer masking material is PDMS, which can be cast upon the master
mold surface, cured with UV radiation, and peeled from the mold to
produce excellent replication of the mold surface.

[0056]FIG. 2 shows a cross-sectional view 200 of another embodiment of an
apparatus 200 useful in patterning of large areas of substrate material.
In FIG. 2, the substrate is a film 208 upon which a pattern is imaged by
radiation which passes through surface relief 212 on a first
(transparent) cylinder 206 while film 208 travels from roll 211 to roll
213. A second cylinder 215 is provided on the backside 209 of film 208 to
control the contact between the film 208 and the first cylinder 206. The
radiation source 202 which is present in the hollow space 204 within
transparent cylinder 206 may be a mercury vapor lamp or another radiation
source which provides a radiation wavelength of 365 nm or less. The
surface relief 212 may be a phase-shift mask, for example, where the mask
includes a diffracting surface having a plurality of indentations and
protrusions, as discussed above in the Background Art. The protrusions
are brought into contact with a surface of a positive photoresist (a
radiation-sensitive material), and the surface is exposed to
electromagnetic radiation through the phase mask. The phase shift due to
radiation passing through indentations as opposed to the protrusions is
essentially complete. Minima in intensity of electromagnetic radiation
are thereby produced at boundaries between the indentations and
protrusions. An elastomeric phase mask conforms well to the surface of
the photoresist, and following development of the photoresist, features
smaller than 100 nm can be obtained

[0057]FIG. 3 shows a cross-sectional view 300 of another embodiment of an
apparatus 300 useful in patterning large areas of substrate material. The
substrate is a film 308 which travels from roll 311 to roll 313. There is
a layer of radiation-sensitive material (not shown) on both the topside
310 of film 308 and the bottom side 309 of film 308. There is a first
transparent cylinder 306, with a hollow center 304, which includes a
radiation source 302, having surface relief 312, which is used to pattern
the top side 310 of film 308. There is a second transparent cylinder 326,
with a hollow center 324, which includes a radiation source 322, having
surface relief 332, which is used to pattern the bottom side 209 of film
308.

[0058]FIG. 4A shows a cross-sectional view 400 of an embodiment of a
transparent cylinder 406 which includes a hollow center area 404 with an
internal source of radiation 402. The surface relief 412 is a conformal
structure which includes polymer film 415 with a patterned surface 413
which is particularly useful for near-field lithography. The polymeric
material of patterned surface 413 needs to be sufficiently rigid that the
pattern will contact a substrate surface to be imaged in the proper
location. At the same time, the polymeric material must conform to the
surface of a radiation-sensitive material (not shown) which is to be
imaged.

[0059]FIG. 4B shows an enlargement of surface 413, which is a surface
relief polymer structure 413 on top of polymeric base material 415. In
FIG. 4B, the polymer base material 415 may be either the same polymeric
material or may be a different polymeric material from the patterned
surface material 413. A transparent conformal material such as a silicone
or PDMS, for example, may be used as polymer film 415, in combination
with a more rigid transparent overlying layer of material, such as PDMS
with a different ratio of mixing components, or polymethyl methacrylate
PMMA, for example. This provides a patterned surface 413, which helps
avoid distortion of features upon contact with a location on the
radiation-sensitive surface of a substrate (not shown), while the
polymeric base material simultaneously provides conformance with the
substrate surface in general.

[0060]FIG. 5A shows a cross sectional view 500 of a transparent cylinder
506, with hollow central area 504 including a radiation source 502, where
the surface 511 presents an alternative embodiment of surface relief 512.
FIG. 5B shows an enlargement of the surface relief 512, which is a thin
metal layer 514 which is patterned with a series of nanoholes 513, where
the metal layer is present on the exterior surface 511 of hollow
transparent cylinder 506. The metal layer may be a patterned layer
adhered to the exterior surface of transparent cylinder 506. In the
alternative, a metal layer may be deposited on the surface of the
transparent cylinder by evaporation or sputtering or another technique
known in the art and then may subsequently etched or ablated with a laser
to provide a patterned metal exterior surface 511. FIG. 5C shows an
alternative surface relief 522 which may be used on the surface of
transparent cylinder 506. Surface relief 522 is formed by metal particles
526 which are applied on an exterior surface 511 of hollow transparent
cylinder 506, or on a transparent film 524 which is attached to the
exterior surface 511 of hollow transparent cylinder 506.

[0061]FIG. 6A is a schematic three dimensional illustration 600 of a
transparent cylinder 604 having a patterned surface 608. A radiation
source (not shown) is present within the interior of transparent cylinder
604. The transparent cylinder 604 is suspended above a substrate 610
using a tensioning device 602, which is shown as springs in illustration
600. One of skill in the art of mechanical engineering will be familiar
with a number of tensioning devices which may be used to obtain the
proper amount of contact between the outer surface 608 of transparent
cylinder 604 and the surface of substrate 610. In one embodiment method
of using the apparatus shown in FIG. 6A, the apparatus is used to image a
radiation-sensitive material (not shown) on a substrate 610, where
substrate 610 is a polymeric film, which may be supplied and retrieved on
a roll to roll system of the kind shown in FIG. 2. The transparent
cylinder 604 is lowered toward the polymeric film substrate (or the
polymeric film substrate is raised), until contact is made with the
radiation-sensitive material. The polymeric film, which is typically
elastomeric will create a Van-der-Walls force bond with the
radiation-sensitive material. The transparent cylinder 604 may then be
raised (or the polymeric film substrate lowered) to a position where
contact remains between the surface 608 of transparent cylinder 604 and
the surface of the radiation-sensitive material, but the tension between
the two surfaces is such that the force placed on the surface 608 is
minimal. This enables the use of very fine nanopatterned features on the
surface 608 of transparent cylinder 604. When the substrate 610 begins to
move, the transparent cylinder 604 will also move, forcing transparent
cylinder 604 to rotate, maintaining the dynamic contact between the
radiation-sensitive material and the underlying polymeric film substrate
610. At any moment of the dynamic exposure, the contact between the
cylinder and a photosensitive layer is limited to one narrow line. Due to
strong Van-der Walls forces between an elastomeric film, for example, on
the cylinder exterior surface and the radiation sensitive (photo
sensitive) layer on the substrate, contact is maintained uniform
throughout the entire process, and along the entire width of the mask
(length) on the cylinder surface. In instances where an elastomeric
material is not present on the cylinder surface which contacts the
substrate, an actuating (rotating) cylinder using a stepper-motor
synchronized with the translational movement of the substrate may be
used. This provides a slip-free exposure process for polymeric or other
cylinder surface material which does not provide strong adhesion forces
relative to the substrate.

[0062]FIG. 6B is a schematic of an embodiment 620 where the radiation used
to accomplish imaging is supplied from a radiation source 612 exterior to
cylinder 604, with the radiation distributed internally 615 and 616
within the hollow portion of the cylinder 604. The radiation may be
directed through the transparent cylinder 604 through the patterned mask
surface 608 toward the radiation-sensitive surface (not shown) of
substrate 608 using various lenses, mirrors, and combinations thereof.

[0063]FIG. 6c is a schematic of an embodiment 630 where the radiation used
to accomplish imaging of the radiation-sensitive material is supplied
from a location which is exterior to the transparent cylinder 604. The
exterior radiation source 612 is focused 617 into a waveguide 618 and
distributed from the waveguide 618 to an optical grating 620 present on
the interior surface 601 of the cylinder 604.

[0064]FIG. 6D is a schematic of an embodiment 640 where the radiation used
to accomplish imaging is supplied from two exterior radiation sources
612A and 612B, and is focused 621 and 619, respectively, upon an optical
grating 620 present on the interior surface 601 of cylinder 604.

[0065]FIG. 7A is a schematic 700 showing the use of multiple cylinders,
such as two cylinders 702 and 704, for example, in series to provide
multiple patterning, which may be used to obtain higher resolution, for
example. The relative positions of the cylinders 702 and 704, for example
may be controlled using data from an interferometer (not shown) in
combination with a computerized control system (not shown).

[0066]FIG. 7B is a cross-sectional schematic 720 showing a pattern 706
created by a first cylinder 702 after imaging and development of a
radiation-sensitive material 710. The altered pattern 708 is after
imaging and development of the radiation-sensitive material 710 where the
altered pattern 708 is created by use of the first cylinder 702 in
combination with a second cylinder 704.

[0067]FIG. 8 shows a cross-sectional schematic of a deformable cylinder
800, the interior 804 of which is pressurized using an apparatus 813
which supplies an optically transparent gas, such as nitrogen, for
example. The outer surface 811 of deformable cylinder 800 may be a
nanopatterned/nanostructured film 812 of a conformable material, which
can be rolled upon a non-flat substrate 805 so that radiation from
radiation source 802 can be precisely applied over a surface 816 of
substrate 805.

[0068]In another embodiment, a liquid having a refractive index of greater
than one may be used between the cylinder surface and a radiation
sensitive (photo sensitive, for example) material present on the
substrate surface. Water may be used, for example. This enhances the
pattern feature's contrast in the photosensitive layer.

[0069]While the invention has been described in detail for a variety of
embodiments above, various modifications within the scope and spirit of
the invention will be apparent to those of working skill in this
technological field. Accordingly, the scope of the invention should be
measured by the appended claim